1. Field of the Invention
This invention relates to a light emitting apparatus and, in particular, to a light emitting apparatus that allows the prevention of a crack etc. caused by a thermal expansion difference between a seal member and a lead due to heat generation in a high-output type light emitting section.
2. Description of the Related Art
A typical light emitting apparatus with an LED (light-emitting diode) as a light source is provided with a transparent seal member that covers in a predetermined range a LED element and a lead. The seal member is of epoxy resin, silicone resin, glass etc. Resins are generally used because they are advantageous in aspects of molding, mass production and cost.
Recently, since blue LED's are developed which have brightness as high as a red or green LED, LED elements are increasingly used for a traffic light, a white lamp etc. Further, high-output type LED elements are developed which have a higher brightness, and a high-output LED of several watts is already produced. Due to its large current flow, the high-output type LED element is subjected to heat generation unignorable in emission characteristic and durability.
In using such a high-output type LED element for an LED lamp, it is known that a resin packaging material is subjected to deterioration such as yellowing of resin, or cracking due to a thermal expansion difference between the respective members, or peeling between the respective members. As the output of LED element increases, such a problem will be worse. Therefore, a high-output LED lamp is desired which has a good durability.
Japanese patent application laid-open No. 11-204838 discloses an LED lamp that a glass packaging material is used to solve the problems in the resin packaging material, such as yellowing of rein, to have improved heat resistance and durability (See FIG. 1 thereof).
However, the conventional light emitting apparatus with glass packaging material has problems as stated below.
In sealing an LED element with a glass material, the glass material is softened and pressed or fused and molded to be integrated with the LED element. The sealed object is subjected to heat in the sealing and thereby it is in thermal expansion. In this state, it is integrated with the glass material without having a stress and then cooled down to room temperature. At this stage, if a thermal expansion difference exists between the LED element and its mounting substrate, its junction interface may be subjected to excessive stress due to a thermal contraction difference. As a result, a bonding failure will be generated therebetween or cracking will be generated in the glass seal material.